Fruits continue to change  and even to breathe  long after we've popped them into our shopping bags.

Within several days of being pollinated, a fruit has created all the cells it ever will. It will get larger, certainly, but that's because the cells expand, not because the plant is making more of them. The cells expand because they are filling up with water.

Dissolved in that water is a rich variety of compounds, including starches, acids and sugars. Technically, at that point a fruit has only matured. It doesn't begin to ripen until it reaches its maximum size.

Ripeness is signaled by a series of changes. Frequently, the skin turns color as the green chlorophyll fades, revealing the underlying pigments. The fruit softens too, as enzymes from within the fruit begin to dissolve the cell walls and the pectin glue that holds them together.

As the cell walls of the fruit dissolve, moisture is released, making the fruit juicy.

At the same time, its chemical compounds intermingle, combining and forming new ones.

Simple sugars like glucose are converted to complex sugars like fructose and sucrose. Fragrances and flavors develop.

Some fruits do not ripen after being picked (berries, cherries, grapes, citrus fruits and watermelon).

One fruit, the avocado, ripens only after it's picked. Some fruits change color and texture and develop more complex flavor after being picked but won't develop any more sweetness (apricots, melons, figs, peaches, nectarines, plums and persimmons).

Some fruits do get sweeter (apples, pears, kiwis, mangoes and papayas). And then there's the banana, which will ripen on the tree or off.

Any fruit  including the tomato  that is still ripening should be stored at room temperature until it has softened and sweetened as much as it can.

Chilling damages the enzymes that help create the flavors in fruits such as tomatoes, peaches, plums, nectarines and apricots.

Other fruits, such as melons, apples, pears and mangoes, are safe to refrigerate after they're fully ripe and sweet.

Joan Namkoong, who usually writes this column, is on leave. This column was excerpted from one by Russ Parsons of the Los Angeles Times. Send shopping queries and new-product information to: Market Basket, The Honolulu Advertiser, P.O. Box 3110, Honolulu, HI 96802. Fax: 525-8055. E:mail: islandlife@honoluluadvertiser.com.